The invention relates to a rotatable magnetic-head unit for recording and/or reproducing signals on/from a magnetic tape. The head unit comprises at least one magnetic head which is situated substantially within the circumference of a rotatable cylindrical drum and around which drum a magnetic tape is wrapped over a part of the drum circumference, which tape is moved past said part of the circumference. The drum is radially supported by at least one spiral-groove bearing. Such a head unit is disclosed in EP 0,180,852 A1, and is radially supported by spiral-groove bearings on the shaft, which also carries the drum. The heads of this unit can only perform a rotary movement.
A head unit in which the magnetic heads, in addition to a rotation, are also capable of performing a translation is known from DE-OS 25 35 780. In this known unit the heads are translated axially relative to the drum in openings which for this purpose are formed in the drum wall, the translation being controlled by means of a cam mechanism. The drum is supported by means of bearings on the drum shaft, which bearings are spaced from and arranged underneath the drum. Such a bearing arrangement on the drum shaft enables the head support to be translated relative to the drum.
In a rotatable head unit stringent requirements are imposed on the radial bearing means of the drum. In this respect it is of particular importance that the magnetic head is positioned accurately relative to the tape. Since the drum is supported at a specific radial and axial distance from the free end of the magnetic head, tolerances in the bearing means will give rise to positional deviations of the magnetic head in said known magnetic-head units. In the case of the translatable magnetic heads in the head unit in accordance with DE-OS 25 35 780 these tolerances are even more manifest on account of the multiple bearing arrangement. It is the object of the invention to ensure an accurate positioning of the magnetic head relative to the tape in such a magnetic-head unit which employs a stable spiral-groove bearing.